Translucent AIN ceramics

An effective processing method was studied to fabricate the translucent AIN ceramics [294]. AIN ceramics with 80 mm diameter have been prepared, which exhibited promising optical performances, e.g., transparent over wavelengths of 0.2-2.2 pm. 

Spectral properties of AIN, including absorption and luminescence in the visible and UV range, actual for practical application are determined by a wide band gap ( g = 6.2 eV) of the material and presence of lattice defects and impurities. In the form of ceramics, AIN maintains almost all properties of single crystals, except that if no special measures are undertaken ceramics are not transparent. Translucent AIN ceramics can be produced by choosing the appropriate concentration and type of sintering aid, such as CaFj [25] or Ca3Al20g [26]. 

Production of translucent AIN ceramics opens a way to new practical applications of this material, particularly as optical components (windows, coating, etc.) in severe application environments. At the same time, translucent AIN ceramics is being studied as a promising laser material. 

Optical spectroscopy of Er " doped into bulk AIN ceramics has been reported [296]. The material was prepared by using hot press sintering of AIN with Et203 and (NH4)(ErE4), which yielded fully dense, translucent, hexagonal AIN. The Er concentration was a small fraction of a percent, and resided in multiple sites, with one type of center dominant. A number of the energy levels of Er " were identified for this center. The temperature dependent fluorescence lifetime was probably radiative, with which the stimulated emission and absorption cross section spectra were derived for the " I... 

Mouzon J, Glowacki E, Oden M (2008) Comparison between slip casting and uniaxial pressing for the fabrieation of translucent yttria ceramics. J Matta- Sci 43 2849-2856 Olhero SM, Miranzo P, Ferreira JMF (2006) AIN ceramics nocessed by aqueous slip casting. J Mater Res 21 2460-2469... 

It seems attractive to use luminescence properties of AIN ceramics for practical application. Though not yet implemented finally, there are several areas of experimental studies aimed at getting developments into actual practical use, such as dosimetry, persistent luminescence, lasing (in the case of translucent ceramics), and others. Some of them will be briefly considered here. 

Using of Translucent Doped AIN Ceramics as Solid-State Lasers... 

Figure 14 AIN ceramics sintered with 3 mass % of Y2O3 (left) and AIN sintered with 0.3 mass % of TiOj and 3 mass % of Y2O3 (right) at 1800°C. Thermal conductivity is 270 W/mK for translucent AIN (left) and 250 W/mK for black AIN (right).

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